Studies of the mesophase development in polymeric fibers during deformation by synchrotron SAXS/WAXD

On-line structural and morphological studies on Kevlar 49 and isotactic pol ypropylene (iPP) fibers during deformation were carried out using synchrotr on small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WA XD). A novel image analysis method was used to extract quantitative fractio ns of the crystal phase, the amorphous phase and a "mesomorphic" (intermedi ate) phase from two-dimensional (2D) WAXD patterns. Results showed that abo ut 20 wt% in the Kevlar 49 fiber had an intermediate mesophase morphology. The transitions between crystal phase, amorphous phase and mesophase were n ot obvious during deformation of Kevlar 49 fiber at room temperatures. 2D S AXS patterns indicated that the superstructure of the Kevlar 49 fiber was f ibril in nature. 2D WAXD results of iPP fibers showed that the alpha -form crystals were quite defective in the initial state and were converted to th e well-known mesomorphic form by drawing at room temperatures. The mesophas e in Kevlar 49 fibers was then compared with that in iPP fibers. The shape of one-dimensional equatorial peak of the mesophase in the iPP fiber was si milar to that in the Kevlar fiber, indicating that the mesophase in both iP P and Kevlar fibers could be similar in some aspects of molecular arrangeme nt. Corresponding 2D SAXS patterns showed that there was no obvious long pe riod in the mesophase of the drawn iPP fiber. We speculate that the constit uents of the mesomorphic fraction extracted in the drawn iPP fibers may con sist of partially oriented bundles of helical chains with random helical ha nds as well as oriented chains with no helical structures (consisting of st ereo/tacticity defects). The latter is similar to the mesophase of rigid ch ains in Kevlar fibers, consisting of only oriented chains with no helical s tructures. (C) 2001 Kluwer Academic Publishers.